Natural swarming suppressed in domesticated bees and hives placed close together enable infected forager bees to spread the mites more quickly. In an 11-month study of 120 commercial colonies, Gloria DeGrandi-Hoffman at the US Department of Agriculture in Tucson, Arizona, and her colleagues found that, although hives had been treated with chemicals to control the mites, 55% of treated hives were still lost.

A model that simulated varroa populations and bee interactions showed that natural swarming, which is suppressed in domesticated bees, keeps varroa populations down. Swarming bees carry the mites away from hives, thus depleting their food supply, and the infected forager bees that raid other hives can quickly spread the mites when hives are placed close together.